1.Field of the invention
The present invention relates to a rack-driven steering apparatus and a rack-driven auxiliary power steering apparatus including the same, and more particularly to a rack-driven steering apparatus by which a steering force transmitted from the steering shaft to the rack bar can be transmitted more accurately and without loss, a separate rack bar supporting unit such as a support yoke and a yoke plug may not be employed, so that noise generated due to an increase of a gap caused by wear of the support yoke after the vehicle travels for a long time or generated by an impact reversely input from a road surface can be prevented and a comfortable steering feeling can be provided to the driver during the steering operation, and a rack-driven auxiliary power steering apparatus including the same.
2. Description of the Prior Art
As generally known in the art, a rack-driven auxiliary power steering apparatus includes a steering system extending from a steering wheel to two wheels, and an auxiliary power apparatus for supplying auxiliary steering power to the steering system.
FIG. 1 is a partially sectional view schematically illustrating a general rack-driven auxiliary power steering apparatus, and FIG. 2 is a sectional view schematically illustrating a portion of the general rack-driven auxiliary power steering apparatus.
The general rack-driven auxiliary power steering apparatus includes a steering system 100 extending from a steering wheel 105 to two wheels 150, and an auxiliary power apparatus 160 for supplying auxiliary steering power to the steering system 160.
The steering system 100 includes a steering shaft 110 an upper end of which is connected to the steering wheel 105 to be rotated together with the steering wheel 105 and a lower end of which is connected to a pinion shaft 120 via a pair of universal joints 115. The pinion shaft 120 is connected to a rack bar 155 through a rack-pinion mechanism 135, and opposite ends of the rack bar 155 are connected to the wheels 150 of the vehicle through tie rods 140 and knuckle arms 145.
In the rack-pinion mechanism 135, a pinion gear 125 formed at a lower end of the pinion shaft 120 and a rack gear 130 formed at one side of an outer peripheral surface of the rack bar 155 are engaged with each other.
The auxiliary power apparatus 160 includes a torque sensor 117 for detecting a steering torque applied to the steering wheel 105 by a driver and outputting an electric signal proportional to the detected steering torque, an electronic control unit (ECU) for generating a control signal based on the electric signal transferred from the torque sensor 117, a motor 165 for generating auxiliary steering power based on the control signal transferred from the electronic control unit, and an auxiliary power unit 170 for transmitting the auxiliary power generated by the motor 165 via a belt 210.
A rack bar supporting unit according to the related art includes a pinion gear 125, a rack bar 155, a support yoke 260, a spring 263, and a yoke plug 265. A rack-pinion type gearbox 210 converts a rotating force input from the steering shaft (not illustrated) as described above into linear movement.
The rack bar 155 is engaged with the pinion gear 125 to convert rotation into linear movement, and a unit for supporting the rack bar 155 toward the pinion gear 125 is installed on a rear surface of the rack bar 155 so that the rack bar 155 and the pinion gear 125 can be smoothly engaged with each other.
The unit for supporting the rack bar 155 includes a support yoke 260, a spring 263, and a yoke plug 265, and the support yoke 260 is located on a rear side of the rack bar 155, that is, at a side opposite to a surface where the rack gear 110 is formed, and is inserted into a cylinder 250 of the gearbox 130 to be moved in a forward/rearward direction perpendicular to the rack bar 155.
The support yoke 260 has a cylindrical shape to be slid forward and rearward in the cylinder 250, and a front part of the support yoke 260 in contact with the rack bar 155 forms a semicircular recess to be attached to a rear side of the rack bar 155.
A spring 263 is disposed at a rear side of the support yoke 260 so that the rack bar 155 and the pinion gear 125 are attached to each other to effectively transmit a force, pushing the support yoke 260 with a predetermined pressure and compensating a gap generated between the rack bar 155 and the pinion gear 125.
The support yoke 260 frictionally slid with respect to a rear surface of the rack bar 155, and is formed of a plastic softer than a general rack bar 155 to prevent the rack bar 155 from being worn out or generating noise due to friction.
The spring 263 accommodated in a spring groove 220 applies a pressure so that the support yoke 260 and the rack bar 155 are attached to each other and is generally a coil spring, and a yoke plug 265 is located on a rear surface of the spring 263 to support the spring 263.
The yoke plug 265 supports the spring 263 to apply a pressure to the support yoke 260. Screw threads and roots are formed in the yoke plug 265 to be fixedly coupled to the gearbox 210 and lock nuts 240 having threads and roots engaged with the threads and roots of the yoke plug 265.
However, in the rack-driven auxiliary power steering apparatus, an engaging force between the pinion gear and the rack gear is low due to a resilient deformation of the rack bar caused by a considerably long shape of the rack bar, making it essential to employ a rack bar supporting unit.
Further, in the rack bar supporting unit according to the related art, if the support yoke is worn out to a degree, a gap is increased, making it difficult to properly support the rack bar.
In addition, a rattle noise may be generated in the support yoke and the yoke plug due to an increase in a gap between the rack bar and the support yoke.
Furthermore, impact noise may be generated as an impact load reversely input from a road surface is not absorbed when the vehicle travels on a rough road such as an unpaved road, and in severe cases, the support yoke or the yoke plug may be damaged.